The use of glass for hurricane windows, security windows, windshields, automobile sidelights, heated windows, and situations where the window is under pressure or could be struck requires that the glass window be laminated to a clear plastic interlayer. A number of these clear plastic materials in sheet form have been developed including polyvinyl butyral (PVB) which is currently the most widely used laminating plastic for automotive windshields and related applications. Alphatic polyurethanes are widely used in aircraft windshields and many military applications, and more recently ionomers which are partially neutralized copolymers of ethylene and acrylic or methacrylic acid are being used for security windows, hurricane glass, bullet resistant glass and any situation requiring high strength and high impact resistance. A significant requirement of all of these clear laminating resins for glass is that they must be inherently stable to sunlight without yellowing which means very little absorption of UV below 380 nm. These materials also must be optically clear.
The growth in demand for increased impact resistance and strength for security and protection along with the need to reduce the weight of glass windows in automobiles, structures, other weight and energy sensitive applications has driven the need to increase the impact strength properties and tensile strength of the finished glass laminate even more. The ionomer class of clear laminating resins has been steadily growing over the past decade with several new products such as Dupont's Sentry 21 which is a sodium neutralized copolymer of ethylene and about 19% methacrylic acid and neutralized to about 25%. Another such product is Noviflex which is a combined sodium and diamine neutralized copolymer of ethylene and about 15% methacrylic acid.
Although these laminating resins perform satisfactory for current applications, most transparent structures utilizing them are made thicker and heavier than desired to gain this performance. Weight saving is always desired with these heavy glass laminates.
Therefore, there is a need for further increasing the adhesion of the glass to the clear plastic laminating layer to the glass to achieving even greater impact resistance of the total glass sandwich laminate by resisting delamination of the composite window under load or high impact in order to reduce the needed weight of the laminate to meet the requirements for the application. In addition, there is a need to also increase the tensile strength of the clear plastic laminating layer to further provide increased impact resistance and strength of the glass window laminate or composite, and to achieve the maximum stiffness and tensile strength and therefore impact resistance per given area weight of the composite. Any improvements in one or both of these properties will permit weight reductions in current laminate configurations or permit higer impact ratings and performance for these higher impact higher strength laminates/composites.
U.S. Pat. No. 5,002,820 to Bolton et al, which is herein incorporated by reference discloses laminated safety glass having thick glass and intermediate film layers which prevent spall larger pieces on impact.
The use of so-called safety glazing or penetration resistant glazing for windows, windshields, and the like using multiple layers of polycarbonate, glass and other resinous materials is well known. For example, glass-polycarbonate resin laminates are described in U.S. Pat. Nos. 4,663,228 and 3,666,614.
In U.S. Pat. No. 3,520,768 there are described laminates of relatively thick glass having a comparatively thin polycarbonate film as the adhesive layer. While generally useful, these laminates suffer from an inability to withstand multiple shots, especially when struck by high velocity bullets such as those fired from rifles. Thus, for example, in prior art laminates utilizing thick forward-facing (impact receiving) glass layers, multiple shots at the thick glass front layer cause much glass cracking and removal of the glass from the laminated structure, making it vulnerable to repeat hits. In order to withstand the repeated hits, the laminates had to be extremely thick and heavy. Even these thick and heavy laminates are not entirely successful, since spalling on the back side or downstream face of said laminates occurred with the resultant danger of injury due to this spalling to persons behind these laminates.
U.S. Pat. No. 4,125,669 to Triebel et al discloses a laminated safety glass which utilizes a thick outside layer of silicate glass which is bonded to a polycarbonate pane of at least 1.5 mm thick.
U.S. Pat. No. 4,312,903 to Molari discloses impact resistant, double glazed structures comprising a plurality of laminae selected from polycarbonate, glass and solid resinous materials. The glass laminae faces the direction of impact and has a thickness from about 30 to 220 mils. The structure utilizes relatively thick outward layers and relatively thin inward layers.